Virtually any non-trivial computer system includes a data backup and data recovery sub-system. Backups serve many purposes, including file restoration in the event of accidental deletion or corruption, or for disaster recovery or compliance purposes. Unfortunately, computer systems are also the target of viruses or other malware. Such viruses and malware can cause disruption in the functioning of the system, or can steal information from the system. Virus scanners operate to detect viruses using signatures. Such signatures can comprise data patterns that indicate a virus may be present in a file. Typically, the data included in a backup will have been scanned for the viruses known at the time of the backup. However, new viruses are constantly being developed.